1. Field of the Invention
The present general inventive concept relates to a method of detecting a bad servo track in a hard disk drive (HDD), and more particularly, to a method of detecting a bad servo track in the HDD by using a servo auto gain control (AGC).
2. Description of the Related Art
Hard disk drives (HDDs) are devices to record data on a disk or reproduce data stored on the disk by using a read/write head. The HDDs are widely used as auxiliary memory devices of computer systems because of their fast access time to a large amount of data.
As the HDD having a high TPI (tracks per inch) and a high BPI (bits per inch) can be embodied, an increase in the data storage capacity and a decrease in the size have been rapidly realized. Also, the application of the HDD has been expanded to laptops, MP3 players, and mobile communication terminals.
The operation of normally reading or writing data with respect to the HDD is initiated by searching for a precise position by reading a servo pattern recorded on a servo track of a disk. The process of recording a servo pattern on a service track is referred to as a servo track write (STW). One of the servo track write process is a method of recording a servo pattern in two steps. According to the method, a reference servo pattern is recorded on a servo track using a servo writer. A final servo pattern is recorded by referring to the reference servo pattern. The reference servo pattern is recorded in units of several tracks, for example, and the final servo pattern is recorded in detail on each track while servo control is performed according to the reference servo pattern. In general, the reference servo pattern is recorded ink a clean room while the final servo pattern is recorded outside the clean room.
A defect in the servo track write generated in the HDD manufacturing process and a defect due to a bad disk (hereinafter, referred to as the “bad servo track”) unavoidably exists in the servo track. Since the bad servo track generates an error in the process of reading and writing data with respect to the disk, the bad servo track needs to be found for the stable use of the HDD. However, since a process time required to find the bad servo track increases as a track density increases, a method of more efficiently finding a bad servo track is needed.
In a conventional technology, a method of checking a signal of a particular portion of a servo sector, such as, a gray code, a burst signal, or a position error signal (PES) to detect a bad servo track has been used. The conventional detection method is useful to detect a bad servo track due to the miswriting of a burst signal, or a broken gray code.
Meanwhile, an error may be generated in the process of reading and writing data with respect to a disk even when the magnitude of a servo signal changes in the same servo track. Thus, a servo track in which a change in the magnitude of a servo signal deviates from a predetermined scope needs to be detected as a bad servo track. However, in the conventional detection method for checking a signal of a particular portion of a servo sector, it is difficult to detect a bad servo track due to the change in the magnitude of a servo signal.